Normalize files (AVI, MP4 & M2TS) for PS3

I have 40+ videos that I have on a external hard drive for my PS3... THey all work and fine. But often i find with these videos, peoples voices are so low that I need to crank up the audio big time. Does anyone know of a good program(s) that can normalize these videos in batch or atleast individually? Its got several different audio (& video types). Of course want to do this without converting files (to of course keep quality the same). I would GREATLY Appreciate any help with this!

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Create a new folder named Source;collect the AVI files and place them in Source.
Create a new, empty folder, called Destination.
Download and install XviD codec.
Download and install Lame mp3.
Download Virtualdub;extract the files and run the program file (there is no installation).

Save the file with the .bat extension instead of .txt, i.e. 'Gain.bat'.
Put the .bat file in the Source folder.
Volume=3 means a gain of 3db
%%A-loud.mp4 means the new file will have the same name with 'loud' added.

If you are using Windows 7, press 'Shift' and right click on Source.
Select 'Open command window here' from the drop down menu.
The black command window opens.
Type gain and press Enter;the files should be processed and new files created.

Damn seriously I never expected this great amount of help so far! you really are going above and beyond seriously! everything you say is working 100% perfectly! AVIs & MP4 worked out perfectly! Genius really! What is great, this isn't just for these videos but every video I get in the future! oooh yea if you do help me out with the m2ts...i also have the mkv version encase that is easier or not.

.....

well spoke bit soon there with mp4. One video worked. Worked exactly correct.. new file created. Than each file got this error. Than tried doing everything over again but still same error. Than tried just doing one video (of those that didn't work) and still the same error game up: